Heat insulators for use in the casting of molten metal

ABSTRACT

COMPOSITIONS OF MATTER SUITABLE FOR USE IN THE PRODUCTION OF HOT TOP LININGS AND THE LIKE COMPRISE 15 TO 50% BY WEIGHT OF FIBROUS MATERIAL, 40 TO 80% OF REFRACTORY FILLER AND 0.5 TO 10% OF A BINDER MATERIAL. THE FIBROUS MATERIAL IS WHOLLY INORGANIC FIBROUS MATEIAL OR CONTAINS UP TO 40% OF ITS WEIGHT OF ORGANIC FIBROUS MATERIAL, AND THE REFRACTORY FILLER CONSISTS IN WHOLE OR IN PART OR DIATOMACEOUS EARTH, BUBBLE ALUMINA, HOLLOW SILICA MICROSPHERES, CALCINED RICE HUSKS OR POZZOLANA (BUBBLED ALUMINOSILICATE).

United States Patent 3,558,591 HEAT INSULATORS FOR USE IN THE CASTING FMOLTEN METAL Michael Robert Yendrek, Cleveland, and Robert RichardDzurilla, Seven Hills, Ohio, assignors to Foseco International Limited,Birmingham, England, a British com- P y No Drawing. Filed July 3, 1969,Ser. No. 839,041 Claims priority, application Great Britain, July 4,1968, 32,019/ 6 8 Int. Cl. B28b 7/36; C08g 37/03, 37/18, 51/04, 51/18U.S. Cl. 260-173 4 Claims ABSTRACT OF THE DISCLOSURE Compositions ofmatter suitable for use in the production of hot top linings and thelike comprise 15 to 50% by weight of fibrous material, 40 to 80% ofrefractory filler and 0.5 to 10% of a binder material. The fibrousmaterial is wholly inorganic fibrous material or contains up to 40% ofits weight of organic fibrous material, and the refractory fillerconsists in whole or in part of diatomaceous earth, bubble alumina,hollow silica microspheres, calcined rice husks or pozzolana (bubbledaluminosilicate).

This invention relates to the art of casting molten metal and moreparticularly to heat insulators for use in the production of metalcastings in foundry practice in which connection it will be morespecifically described. How ever the heat-insulators may be used inconnection with the production of steel ingots.

In the casting of molten metal into a mould to form a metal casting itis important to ensure that the head metal, i.e. the metal in the feederheads, risers and like parts of the mould, does not solidify too quicklysince if it does the feed and molten metal, to compensate for thecontraction of the main body of the cast metal on cooling andsolidification, will be hampered and the resulting casting may containimperfections such as fissures and cavities. It is accordingly thepractice to line the feeder heads, risers and the like of casting mouldswith a composition which acts as a barrier to the loss of heat from thehead metal, e.g. a heat insulating composition or a composition whichcontains ingredients which react exothermically when fired by the heatof the molten metal thereby positively to supply heat to the head metal.

In recent years increasing use has been made for the purpose of liningcompositions which comprise a grannular or powdered refractory heatinsulating material, organic fibrous material and a binder material.Whilst various organic fibrous materials have been employed it has beenfound very convenient, on basis of economy, to use either anintrinsically cheap organic fibrous material such as paper pulp or awaste synthetic fibrous material. It has also been proposed to includein such compositions a small proportion of refractory fibrous material,e.g. asbestos, slag wool or mineral wool.

The compositions in question must, in order to be most effective, be ofsubstantially homogeneous character and the procedure which has commonlybeen adopted, therefore, is to make an aqueous slurry containing thegranular or powdered refractory, the organic fibrous material,refractory fibrous material if required, end binder, and then byexpressing the liquid from the slurry to make suitable shapes, e.g.sleeves of the solid ingredients which, when dried and preferablystoved, are rigid structures, the binder serving to bind together theother ingredients. Thus the slurry may be brought against a wire meshand the liquid expressed through the mesh so that a body of the solidingredients which do not pass the mesh is built up on the mesh surface.

3,558,591 Patented Jan. 26, 1971 ice The binder may be any materialknown per se for use in the production of shaped bodies of refractorymaterial for the purpose indicated herein, e.g. an inorganic binder suchas sodium silicate or an organic binder such as a natural gum, e.g.dextrin, or a cereal flour, e.g. wheat flour, or a synthetic resinousmaterial, preferably a thermosetting resin such as a urea-formaldehyde,phenol formaldehyde or furane resin.

Whilst compositions formulated as described above are in widespread useand have many advantages, they do not always have a sufiiciently highdegree of refractoriness for use when handling high melting metals.Moreover their heat insulating characteristics are .not always as goodas is desired.

It is an object of the present invention to provide new compositionswhich may be used for lining feeder hands, risers and the like of metalcasting moulds and which have improved characteristics.

According to the present invention there are provided compositions ofmatter, suitable for use in the production of linings as aforesaid whichcomprise 15 to 50% by weight of fibrous material, 40 to of refractoryfiller and 0.5 to 10% of a binder material, the said fibrous materialbeing wholly inorganic fibrous material or containing up to 40% of itsweight of organic fibrous material and the said refractory fillerconsisting in whole or in part of lightweight filler selected fromdiatomaceous earth, bubble alumina, hollow silica microspheres, calcinedrice husks and pozzolana (bubbled aluminosilicate).

Preferably according to the invention the content of fibrous material is20 to 30% by weight of the composition.

The invention further provides a method for the production of shapedelements suitable for use as aforesaid which comprises forming anaqueous slurry of the ingredients of a composition as just defined, andexpressing the liquid therefrom to deposit a body of the solidingredients in the required shape.

The invention further provides a method for lining a feeder head, riseror the like of a metal casting mould which comprises forming a saidlining of one or more shaped elements formed of a composition ashereinbefore set forth, and preferably one made by the methodhereinbefore set forth.

Within the field of compositions of this invention there may be providedcompositions which are refractory enough to be used with molten steel,which are economic to manufacture (due to their light weight and thefact that a substantial proportion of the relatively expensive organicfibre materials may be replaced by the relatively inexpensive organicfibrous materials), and which has a high heat insulating capacity.

Referring now to the individual ingredients of the composition, therefractory filler consists of one or more of the lightweight fillersnoted above, alone or in association with other granular or powdered noncarbonaceous refrac tory fillers, for example, silica flour, olivine,chamotte, alumina, or any refractory silicate. The grain size of therefractory filler may vary widely but a material which will pass a 325E88 mesh has been found particularly satisfactory.

The fibrous material included in the compositions of the presentinvention consists, to the extent of at least 60% of its weight, ofinorganic fibres such as calcium silicate, aluminum silicate or (morepreferably) aluminosilicate fibres, asbestos, slag wool, rock wool,mineral wool or metal fibres.

Organic fibrous material when present may be, for example, wood pulp(paper pulp) or wood flour but larger fibered material may be employedif desired, e.g. cotton waste, rag stock or waste synthetic staplefibre, for example of nylon, polyester or acrylonitrile fibre. It willbe appreciated that the longer-fibred materials tend to be moreeffective in increasing the strength of the final composition.

The binder material may be any of those shown per se for use in theproduction of shaped elements for the purposes indicated, e.g. sodiumsilicate, gums, cereal flours, or thermosetting resin. It is preferredto employ thermosetting resins and generally a combination ofphenolformaldehyde and urea-formaldehyde resins has been found mostsuitable.

If desired, shaped elements made of the compositions of this inventionmay be given a surface coating of a compact ceramic refractory material,e.g. deposited from a dressing comprising zircon flour, to increase theresistance of the elements to metal penetration.

The following examples will serve to illustrate the invention:

EXAMPLE 1 An aqueous slurry is formed of 90 parts by Weight and parts byweight of a composition consisting of:

Percent by weight Diatomaceous earth (-325 BSS mesh) 50 Paper fibre 10Mineral wool- 30 Phenol-formaldehyde resin 8 Urea-formaldehyde resin 2Example 1 was repeated except that in place of the diatomaceous earth,the same weight of calcined rice husks was used. Permeability of theslab was very high, transverse strength 75 p.s.i. and density 0.37gm./cc.

Feeder head performance was similar to that of the material of Example-1.

EXAMPLE 3 Example 1 was repeated except that in place of thediatomaceous earth, the same weight of calcined rice zolana was used.Permeability of the slab was very high, transverse strength 70 p.s.i.and density 0.35 gm./cc.

Feeder head performance was similar to that of the material of Example1.

Whilst the invention has been described with particular reference to usewith metal casting moulds it is to be understood that the compositionsmay also be used for lining the head of an ingot mould or for lining ahead box fitted to such mould.

It is observed that the presence in riser sleeves and like shapes ofcarbon or carbonaceous filler (e.g. coke dust), is not desirable whencasting steel; the presence of carbon tends to affect the finalcomposition and properties of the cast metal.

We claim as our invention:

1. A heat-insulating composition of matter suitable for use in theproduction of hot top linings and the like which consists essentially of15 to 50% by Weight of an inorganic fibrous material selected from thegroup consisting of calcium silicate, aluminium silicate,aluminosilicate, asbestos, slag wool, rock wool, mineral wool and metalfibers, with the proviso that an organic fibrous material selected fromthe group consisting of wood pulp, wood flour, cotton Waste, rag stock,and waste synthetic staple fiber may be substituted for up to 40% of theinorganic fibrous material, 40 to of a light weight refractory fillerselected from the group consisting of diatomaceous earth, bubblealumina, hollow silica microspheres, calcined rice husks and pozzolanaand 0.5 to 10% by weight of a binder material selected from the groupconsisting of sodium silicate, natural gums, cereal flour andthermosetting resins.

2. A composition according to claim 1 wherein the fibrous materialconstitutes 2030% by weight of the composition.

3. A composition according to claim 1 wherein part of the refractoryfiller consists of a particulate refractory filler selected from thegroup consisting of silica flour, olivine, chamotte, alumina andrefractory silicates.

4. A composition according to claim 1 wherein the binding agent is amixture of phenoland urea-formaldehyde resins.

References Cited UNITED STATES PATENTS 2,798,818 7/1957 Pletsch et al.106-382 3,123,878 3/1964- Davidson 106-3822 3,230,056 1/1966 Arant et al10638.22 3,300,322 1/1967 De Geer 10638.35

WILLIAM H. SHORT, Primary Examiner E. WOODBERRY, Assistant Examiner US.Cl. X.R.

